Quench protected structured superconducting cable

ABSTRACT

Quench protected structured (QPS) superconducting cables, methods of fabricating the same, and methods of bending the same are disclosed. The methods of bending the QPS superconducting cables can be employed to produce windings. The QPS superconducting cables can rapidly drive a distributed quench to a normal conducting state in a superconducting cable if a region of the cable spontaneously quenches during high current operation.

CROSS-REFERENCE TO A RELATED APPLICATION

The present application claims the benefit of U.S. ProvisionalApplication Ser. No. 62/036,146, filed Aug. 12, 2014, which isincorporated by reference herein in its entirety, including any figures,tables, and drawings.

BACKGROUND

Cable in conduit (CIC) geometries are currently used to fabricatesuperconducting cables. Quenching is a problem in superconductingcables. Quenching is an abnormal termination of magnet operation thatoccurs when part of the superconducting cable enters a resistive state.The part of the superconducting cable in which the quench occursundergoes rapid Joule heating, causing regions of the superconductingcable surrounding the quench to enter a resistive state. This causesadditional Joule heating, leading to a chain reaction, in whichincreasingly large sections of the superconducting cable enter aresistive state. Existing techniques are not able to externally induce adistributed quench in a CIC conductor and instead either add asubstantial amount of stabilizing copper within the CIC conductor orlimit the overall performance to avoid the potential for a quench todamage the windings.

BRIEF SUMMARY

The subject invention provides novel and advantageous quench protectedstructured (QPS) superconducting cables, methods of fabricating thesame, methods of using the same, and methods of bending the same thatcan solve the aforementioned problems. Embodiments of the subjectinvention can rapidly force a distributed quench throughout asuperconducting cable, which is beneficial at least in part because anyJoule heating and/or voltage fluctuation can be distributed throughoutthe superconducting cable rather than concentrated at a particularpoint. Rapidly forcing a distributed quench throughout a superconductingcable avoids or inhibits the damage likely to otherwise occur if aquench occurs spontaneously at a single point in the superconductingcable.

In one embodiment, a QPS superconducting cable can include: a springtube; a plurality of superconducting wires disposed around the springtube; and a sheath surrounding the plurality of superconducting wiresand the spring tube, wherein the spring tube comprises a plurality ofperforations. The QPS superconducting cable can further include aplurality of quench heater wires, wherein each quench heater of theplurality of quench heater wires is a resistive wire that generates heatas current passes through it. The plurality of quench heater wires canbe distributed among the plurality of superconducting wires within thesheath or provided external to the sheath.

In another embodiment, a method of bending a QPS superconducting cablecan include: evacuating the spring tube to create at least a partialvacuum; filling the spring tube with water; cooling the QPSsuperconducting cable to freeze the water; bending the QPSsuperconducting cable; warming the QPS superconducting cable to roomtemperature; draining the water; and evacuating the QPS superconductingcable to at least a partial vacuum to remove any residual water. Such amethod can result in bending the QPS superconducting cable to an angleof about 180° with a ratio of radius of curvature to sheath radius of7:1 or less.

In another embodiment, a method of compacting a sheath of a QPSsuperconducting cable onto internal components of the QPSsuperconducting cable can include: drawing the sheath through a formingdie in a succession of reducing deformations until the plurality ofsuperconducting wires compress the spring tube by a small displacementso that each of the plurality of superconducting wires are immobilizedin an annular space between the sheath and the spring tube, and each ofthe neighboring wires of the plurality of superconducting wires arecompacted against one another so that a controlled electrical contact isestablished among the neighboring wires of the plurality ofsuperconducting wires.

Further details and advantages of the disclosure become apparent in thefollowing description of various preferred embodiments by way of theattached drawings. The drawings are included for purely illustrativepurposes and are not intended to limit the scope of the presentdisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view, a schematic view, and across-sectional image of QPS superconducting cables according toembodiments of the subject invention.

FIG. 2 shows a cross-sectional view illustrating stress on components ofa QPS superconducting cable according to an embodiment of the subjectinvention, after a sheath is placed on the components.

FIG. 3 shows a schematic view illustrating von Mises stress oncomponents of a QPS superconducting cable according to an embodiment ofthe subject invention.

FIG. 4 shows a flow diagram of a process for bending a QPSsuperconducting cable according to an embodiment of the subjectinvention.

FIG. 5 shows a cross-sectional view and a schematic view of a QPSsuperconducting cable applied to be used in a dipole.

FIG. 6 shows a simulation of heat transfer within the coils of thedipole shown in FIG. 5.

FIG. 7 depicts a simulation of the von Mises stress in a winding of thedipole shown in FIG. 5.

FIG. 8A shows a schematic view of a QPS superconducting cable accordingto an embodiment of the subject invention used for superconductingmagnet energy storage.

FIG. 8B shows an overhead image of the financial district in New YorkCity.

FIG. 9A shows a schematic view of a QPS superconducting cable accordingto an embodiment of the subject invention used for a high-powertransmission line.

FIG. 9B shows a schematic view of a QPS superconducting cable accordingto an embodiment of the subject invention used for a high-powertransmission line.

FIG. 10A shows a schematic view of a QPS superconducting cable accordingto an embodiment of the subject invention.

FIG. 10B shows a cross-sectional view of a QPS superconducting cableaccording to an embodiment of the subject invention.

FIG. 11 shows a cross-sectional view of a QPS superconducting cableaccording to an embodiment of the subject invention.

FIG. 12 shows images of fabricating a QPS superconducting cableaccording to an embodiment of the subject invention.

FIG. 13 shows images of QPS superconducting cables according toembodiments of the subject invention.

FIG. 14 shows alternative options for forming continuous supportspiders.

FIG. 15 shows a schematic view of a rope-on-rope configuration.

DETAILED DESCRIPTION

The subject invention provides novel and advantageous quench protectedstructured (QPS) superconducting cables, methods of fabricating thesame, methods of using the same, and methods of bending the same thatcan solve the aforementioned problems. Embodiments of the subjectinvention can rapidly force a distributed quench throughout asuperconducting cable, which is beneficial at least in part because anyJoule heating and/or voltage fluctuation can be distributed throughoutthe superconducting cable rather than concentrated at a particularpoint. Rapidly forcing a distributed quench throughout a superconductingcable avoids or inhibits the damage likely to otherwise occur if aquench occurs spontaneously at a single point in the superconductingcable.

When the term “about” is used herein, in conjunction with a numericalvalue, it is understood that the value can be in a range of 95% of thevalue to 105% of the value, i.e. the value can be +/−5% of the statedvalue. For example, “about 1 kg” means from 0.95 kg to 1.05 kg.

FIG. 1 shows a cross-sectional view (left), a schematic view (middle),and a cross-sectional image (right) of QPS superconducting cablesaccording to embodiments of the subject invention. Referring to FIG. 1,in an embodiment, a QPS superconducting cable 100 can include aplurality of superconducting wires 114, a plurality of quench heaterwires 110, and a spring tube 118. The spring tube 118 can beinterspersed among the plurality of superconducting wires 114 and/or theplurality of quench heater wires 110. For example, the spring tube 118can be positioned in the middle (e.g., in a radial sense of the QPSsuperconducting cable) of the superconducting wires 114 and/or thequench heater wires 110. The spring tube 118 can be positioned along ornear a central axis of the QPS superconducting cable. A sheath 106 canbe included and can encase the superconducting wires 114, the quenchheater wires 110, and the spring tube 118. In a further embodiment, thespring tube 118 can contain perforations. The spring tube 118 can befilled with a material, for example a cryogenic material, which can thenpass through the perforations in the spring tube 118, fillinginterstitial space 116 separating the spring tube 118, the plurality ofsuperconducting wires 110, and the plurality of quench heater wires 110.

The plurality of quench heater wires 110 are optional and can beexcluded. If present, the heater wires 110 can provide the heatnecessary to rapidly force quench throughout the QPS superconductingcable 100. If a quench is detected in the QPS superconducting cable 100,the plurality of quench heater wires 110 can be activated to heat theQPS superconducting cable 100 to mitigate damage to the QPSsuperconducting cable 100 induced by a singular quench point.

Although FIG. 1 depicts a QPS superconducting cable 100 with a pluralityof quench heater wires 110 interspersed among a plurality ofsuperconducting wires 114, in another embodiment, the quench heaterwires 110 can be located externally to the sheath 106. Whether thequench heater wires 110 are interspersed among the plurality ofsuperconducting wires 114 or located on the surface of the sheath 106can depend on, e.g., the quench velocity v_(q) with which a quench thatstarts at one location in a winding can propagate along the winding. Thedynamics of quench propagation are a balance between the Joule heatingin the quenched region as current bypasses through the conducting (e.g.,copper) portion of a wire composition, the heat conduction through thatcopper, the heat capacity (˜T³) of the wire, and the transitiontemperature at which a superconducting segment is quenched to the normalstate.

In an embodiment, the interstitial space 116 within the sheath 106 canbe impregnated with a material. For example, the interstitial space 116can be impregnated with an epoxy, though embodiments are not limitedthereto. The interstitial space 116 can be impregnated with the materialvia, for example, a vacuum method, though embodiments are not limitedthereto. In one embodiment, the interstitial space 116 within the sheath106 can be vacuum impregnated with epoxy.

The superconducting wires 114 and/or quench heater wires 110 can havevoids within the wires themselves. In one embodiment, the voids withinthe superconducting wires 114 and/or quench heater wires 110 can beun-impregnated. In an alternative embodiment, the voids within thesuperconducting wires 114 and/or quench heater wires 110 can beimpregnated (e.g., vacuum impregnated) with a material.

Referring to the image (right-hand side) in FIG. 1, a QPSsuperconducting cable 100 can have a small size. The image of the wiredepicted shows a diameter, including the sheath 106 of 9 mm, with eachsuperconducting wire 114 having a diameter of 1.2 mm. These diametersare provided for exemplary purposes only and should not be construed aslimiting. The sheath 106, each superconducting wire 114, the spring tube118, and each quench heater wire 110 can have a diameter of, forexample, any of the following values, about any of the following values,at least any of the following values, at least about any of thefollowing values, not more than any of the following values, not morethan about any of the following values, or within any range having anyof the following values as endpoints (with or without “about” in frontof one or both of the endpoints), though embodiments are not limitedthereto (all numerical values are in percentage by weight (mm)): 0.01,0.1, 0.5, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2,3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30,35, 40, or 50, though embodiments are not limited thereto. Of course,the diameter of the sheath will be greater than that of the spring tube118 and each superconducting wire 114 for any given QPS superconductingcable 100 (in cases where the quench heater wires 110 are present withinthe sheath 106, the sheath 106 will also have a larger diameter thanthat of each quench heater wire 110).

The superconducting wires 114 can be any suitable shape (e.g., flatribbons or cylindrical). The superconducting wires 114 can include, forexample, at least one of the following materials: Cu, Ag, Au, Pt, Pd,NbTi, NbTi/Cu, Nb₃Sn, Nb₃Sn/Cu, Bi-2212, Bi-2212/Ag, MgB₂, Monel,MgB₂/Monel, ferropnictide, Bi-2223, YBCO, and rare-earth-basedbariumcarbonates (ReBCO), though embodiments are not limited thereto.

In an embodiment, a QPS superconducting cable can further include atleast one layer of thermally conducting and electrically insulating tapearound (e.g., spiral-wrapped around) the plurality of superconductingwires, the plurality of quench heater wires, and the spring tube withinthe sheath.

In an embodiment, a QPS superconducting cable can further include aplurality of resistive wires cabled with the plurality ofsuperconducting wires so that a first resistive wire of the plurality ofresistive wires is located at a V-crevice formed between two contiguoussuperconducting wires of the plurality of superconducting wires, so thata radius of an outermost point on the first resistive wire from thecenter of the cable equals or is approximately equal to the radius (fromthe center of the cable) of an outermost point on the two contiguoussuperconducting wires. The plurality of resistive wires can be equal innumber to the plurality of superconducting wires. Each resistive wire ofthe plurality of resistive wires can include a metal alloy (e.g.,stainless steel of Monel). In a further embodiment, the plurality ofresistive wires can be coated with an insulator. The insulator can be,for example, a ceramic, a glass, and/or a polymer (e.g., a uniform filmof a ceramic, a glass, or a polymer).

In an embodiment, the sheath can include a fiber-glass cloth and/or anda fiberglass tape applied to an outer surface of the internal components(e.g., the plurality of superconducting wires).

QPS superconducting cables of the subject invention are designed tomanage stresses. The mechanical support is provided by the stressmanagement that is integrated into the QPS superconducting cable itself.The material or materials from which the sheath is fabricated can beselected to provide robust mechanical strength to support the hoopstress of Lorentz loading and the accumulation of load passed radiallythrough multiple layers of a winding. FIG. 2 shows stress on componentsof a QPS superconducting cable according to an embodiment of the subjectinvention, after a sheath is placed on the components to compress thewires (e.g., superconducting wires) against the spring tube. FIG. 3shows von Mises stress on components of a QPS superconducting cable inwhich the interstitial space (116) within the sheath is vacuumimpregnated with epoxy and the voids within the superconducting wiresand quench heater wires are un-impregnated. Referring to FIG. 2, theplastic deformation of the sheath and the local elastic compression ofthe spring tube are evident; the plurality of superconducting wires andthe plurality of quench heater wires themselves can be immobilized withvery little internal stress. Referring to FIG. 3, the sheath can act asa stress bridge to protect the plurality of superconducting wires andquench heater wires from being strained.

The superconducting wire(s) used in the QPS superconducting cable can beany suitable material, including but not limited to NbTi, MgB₂, andNb₃Sn. The choice of material for the superconducting wire(s) used inthe QPS superconducting cable can depend on the specific application forwhich the QPS superconducting cable is used. Table 1 shows a pluralityof non-limiting applications (columns) for a QPS superconducting cableaccording to embodiments of the subject invention. The rows showexamples of parameter values (units are shown in the far-right column,when applicable) for each application, and the first row shows examplematerials for the superconducting wire(s) for each application. Thevalues and materials provided for each application are for exemplarypurposes only and should not be construed as limiting. Referring toTable 2, if the QPS superconducting cable is to be used as a particlecollider dipole, then the plurality of superconducting wires can includeNbTi. If the QPS superconducting cable is to be used for magnetic energystorage, then the plurality of superconducting wires can include MgB₂.In each case listed in Table 1, the superconducting wires can alsoinclude another conductive element (e.g., copper).

TABLE 1 Example parameters for different applications of QPSsuperconducting cable Collider Proton Magnetic Transmission Tokamakdipole therapy gantry energy storage line solenoid superconductor NbTiMgB₂ MgB₂ MgB₂ Nb₃Sn Operating field 4.5 3 3 1 13 T Cable current 20 5015 40 kA Operating temp 4.5 15 20 20 5 K # wires 17 11 25 25 6 × 180 #turns 10 40 180 1 # windings 2 2 1 3 Quench velocity 83 6.5 6.5 m/s Unitlength 20 3.1 4 100 m Stored energy 1.3 0.2 100 MJ Quench protectExternal Internal wires External strips Internal wires @ ends

In some embodiments, the QPS superconducting cable can include asingle-layer array of superconducting wires cabled together onto aspring tube. The superconducting wires can be cabled together with, forexample, a twist pitch. The spring tube can be a thin-walled springtube. For example, the spring tube can be a gold (Au) spring tube,though embodiments are not limited thereto.

In one embodiment, a QPS superconducting cable can include asingle-layer array of superconducting wires cabled together onto aspring tube. The superconducting wires can be cabled together with, forexample, a twist pitch. The spring tube can be a thin-walled spring tube(e.g., a gold spring tube). The QPS superconducting cable can befabricated by cabling strands of NbTi/Cu superconducting wires onto athin-walled (e.g., 150 μm) perforated Monel spring tube, and insertingthe superconducting wires and spring tube into an outer Monel sheath.The Monel sheath can then be drawn down onto the strands of NbTi/Cusuperconducting wires and the thin-walled perforated Monel spring tubeto load the strands into compression against the Monel spring tube sothat they are immobilized. Cryogen can flow through the spring tubeduring operation and can permeate the interstitial space between thesuperconducting wires and spring tube by flowing through theperforations in the spring tube. The sheath can be formed using, forexample, the method of continuous tube-forming (CTFF) disclosed in U.S.Pat. No. 6,687,975, which is incorporated herein by reference in itsentirety. The CTFF method can include forming a metal strip into acontinuous tube and seam-welding the strip using a method that does notdamage the superconducting wires inside. Such a method allows forsheathing of a cable of any length without having to pull it through anexisting sheath tube. The sheath can then be drawn down onto the cableto compress the cable wires against the spring tube and immobilize them.Other methods can be used to extrude the plurality of superconductingwires, a plurality of quench heater wires, and the spring tube through asheath.

Many applications using the QPS superconducting cable require the QPSsuperconducting cable to be bent. FIG. 4 shows a flow diagram of aprocess for bending a QPS superconducting cable according to anembodiment of the subject invention. In an embodiment, the QPSsuperconducting cable can be bent to any required angle (e.g., 180°)with a small radius of curvature, minimal to no deformation, and littleto no crushing of the internal components or geometry of the QPSsuperconducting cable. Referring to FIG. 4, a spring tube can beevacuated to create at least a partial vacuum 502. The spring tube canthen be filled with a liquid (e.g., an aqueous solution or water) 506.In a specific embodiment, the spring tube can be filled with liquidthroughout its length using a syringe and a long flexible tube so thatthe liquid is inserted into the middle of the spring tube and excludesair towards both ends. Such a procedure avoids or limits trappingbubbles, which could produce a local stress concentration and collapseof the QPS superconducting cable during bending. When the QPSsuperconducting cable is filled with liquid (e.g., water), at least aportion of the liquid can be purged with agitation and a mild vacuum canbe applied to fill the liquid into the interstitial space (116). The QPSsuperconducting cable can be cooled to freeze the liquid 510. The QPSsuperconducting cable can then be bent to the desired angle 514. The QPSsuperconducting cable can then be warmed (e.g., to room temperature).The liquid can then be drained from the QPS superconducting cable 522. Avacuum (or partial vacuum) can then be used to at least partiallyevacuate the QPS superconducting cable to remove any residual liquidfrom the QPS superconducting cable 526. Though FIG. 4 mentions water asthe liquid, this is in an exemplary embodiment and should not beconstrued as limiting.

In a specific embodiment, 180° bends were made with a bend radius of 32mm in a QPS superconducting cable with a sheath radius of 4.5 mm, givinga ratio of 7:1 (bend radius:sheath radius). The ratio of bend radius(radius of curvature) to sheath radius can be, for example, any of thefollowing values, about any of the following values, at least any of thefollowing values, at least about any of the following values, not morethan any of the following values, not more than about any of thefollowing values, or within any range having any of the following valuesas endpoints (with or without “about” in front of one or both of theendpoints), though embodiments are not limited thereto (all numericalvalues are dimensionless): 20:1, 19:1, 18:1, 17:1, 16:1, 15:1, 14:1,13:1, 12:1, 11:1, 10:1, 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, or 2:1,though embodiments are not limited thereto. For example, in manyembodiments, the ratio of bend radius (radius of curvature) to sheathradius is 7:1 or less.

In an embodiment, a method of fabricating a QPS superconducting cablecan include fabricating the cable as described by individuallyfabricating the components (or collectively fabricating some or all ofthe components and separately fabricating others, individually orcollectively). The components can then be combined, and the sheath canbe provided around the superconducting wires and the spring tube (and insome cases the quench heater wires.

FIG. 12 shows images of fabricating a QPS superconducting cableaccording to an embodiment of the subject invention. Referring to FIG.12, in an embodiment, superconducting wires can be twist-pitch cabledonto a spring tube (top left). CTFF can be performed to provide thesheath (bottom left). The sheath tube can be drawn down onto the cableto compress the wires against the spring tube, and the QPS cable can bebent to 180°. The inset shows the finished bend.

QPS superconducting cables of embodiments of the subject invention, aswell as the methods of fabricating the same and bending the same, can beadvantageously used in many different applications. For example, a QPSsuperconducting cable as described herein can be used: in a dipolemagnet (e.g., a 4.5 T dipole magnet); as compact beam gantries for usein proton beam cancer therapy; in magnetic energy storage systems; intransmission lines; and to form high strength structured cable formulti-turn windings with large hoop stress.

In an embodiment of the subject invention, quench protection can beprovided by an external heater at the ends of all turns. This can beused, for example, in a winding for cables used in high-stored-energymagnets in which the quench velocity is fast (e.g., NbTi), so that thelength of cable for each quench heater is kept minimum.

In an embodiment, quench protection can be provided via a plurality ofquench heater wires (e.g., a layer of insulated quench heater wires)cabled with the superconducting wires, so that quench can be forcedsimultaneously everywhere. This can be used, for example, in a windingfor windings in which the quench velocity is slow (e.g., Nb₃Sn, MgB₂,Bi-2212).

In an embodiment, a high-power transmission line can include QPSsuperconducting cables as disclosed herein (e.g., three cables) that canbe supported within a corrugated vacuum shell, with provision for highdielectric strength among cables, in a geometry that is robust butflexible.

For windings that are expected to experience large mechanical forces(e.g., solenoid and tokamak windings), the structure can be designed toincorporate a resistive (e.g., paper) insulating sheath and/or a supportspider with high compressive strength but significant flexibility forwinding. The twist pitch of the wire and the cylindrical shell geometryof the cable can naturally minimize AC losses for applications thatrequire cyclic or alternating current in the windings.

The subject invention includes, but is not limited to, the followingexemplified embodiments.

Embodiment 1

A quench protected structured (QPS) superconducting cable, comprising:

a spring tube;

a plurality of superconducting wires disposed around the spring tube;and

a sheath surrounding the plurality of superconducting wires and thespring tube,

wherein the spring tube comprises a plurality of perforations.

Embodiment 2

The QPS superconducting cable according to embodiment 1, wherein thesheath is applied using a continuous tube forming technique.

Embodiment 3

The QPS superconducting cable according to embodiment 2, wherein thecontinuous tube forming technique is the technique of U.S. Pat. No.6,687,975.

Embodiment 4

The QPS superconducting cable according to any of embodiments 1-3,further comprising a plurality of quench heater wires, wherein eachquench heater of the plurality of quench heater wires is a resistivewire that generates heat as current passes through it.

Embodiment 5

The QPS superconducting cable according to embodiment 4, wherein theplurality of quench heater wires are distributed among the plurality ofsuperconducting wires within the sheath.

Embodiment 6

The QPS superconducting cable according to embodiment 4, wherein theplurality of quench heater wires are provided external to the sheath.

Embodiment 7

The QPS superconducting cable according to embodiment 6 wherein theplurality of quench heater wires are distributed on an outer surface ofthe sheath.

Embodiment 8

The QPS superconducting cable according to any of embodiments 1-7,wherein the plurality of superconducting wires are cabled with a twistpitch around the spring tube and are confined within the sheath.

Embodiment 9

The QPS superconducting cable of any of embodiments 1-8, wherein thespring tube is filled with a cryogen that passes through the pluralityof perforations in the spring tube and thereby fills interstitial spacebetween the sheath and the plurality of superconducting wires.

Embodiment 10

The QPS superconducting cable according to any of embodiments 1-9,wherein the plurality of superconducting wires includes at least one ofthe following materials: NbTi/Cu; Nb₃Sn/Cu; Bi-2212/Ag; MgB₂/Monel;ferropnictide; Bi-2223; YBCO; and rare-earth-based barium carbonates(ReBCO).

Embodiment 11

The QPS superconducting cable according to any of embodiments 1-10,wherein each superconducting wire of the plurality of superconductingwires is cylindrical.

Embodiment 12

The QPS superconducting cable according to any of embodiments 1-10,wherein each superconducting wire of the plurality of superconductingwires is a flat ribbon.

Embodiment 13

The QPS superconducting cable according to any of embodiments 1-12,further comprising at least one layer of thermally conducting andelectrically insulating tape spiral-wrapped around the plurality ofsuperconducting wires and the spring tube (and the plurality of quenchheater wires, if present and within the sheath) within the sheath.

Embodiment 14

The QPS superconducting cable according to any of embodiments 1-13,further comprising a plurality of resistive wires cabled with theplurality of superconducting wires so that a first resistive wire of theplurality of resistive wires is located at a V-crevice formed betweentwo contiguous superconducting wires of the plurality of superconductingwires, so that a radius of an outermost point on the first resistivewire from the center of the cable equals the radius of an outermostpoint on the two contiguous superconducting wires.

Embodiment 15

The QPS superconducting cable according to embodiment 14, wherein theplurality of resistive wires is equal in number to the plurality ofsuperconducting wires.

Embodiment 16

The QPS superconducting cable according to any of embodiments 14-15,wherein the plurality of resistive wires is coated with an insulator.

Embodiment 17

The QPS superconducting cable according to any of embodiments 14-16,wherein each resistive wire of the plurality of resistive wirescomprises a metal alloy.

Embodiment 18

The QPS superconducting cable according to embodiment 17, wherein themetal alloy comprises stainless steel of Monel.

Embodiment 19

The QPS superconducting cable according to any of embodiments 16-18,wherein the insulator is a uniform film of any of a ceramic, a glass,and a polymer.

Embodiment 20

The QPS superconducting cable according to any of embodiments 1-19,wherein the sheath comprises any one of: a fiber-glass cloth; and afiberglass tape applied to an outer surface of the plurality ofsuperconducting wires.

Embodiment 21

A method of bending a QPS superconducting cable according to any ofembodiments 1-20, wherein the method comprises the steps of:

evacuating the spring tube to create at least a partial vacuum;

filling the spring tube with a liquid;

cooling the QPS superconducting cable to freeze the liquid;

bending the QPS superconducting cable;

warming the QPS superconducting cable to room temperature;

draining the liquid; and

evacuating the QPS superconducting cable to at least a partial vacuum toremove any residual liquid.

Embodiment 22

The method according to embodiment 21, wherein the liquid is water.

Embodiment 23

The method according to any of embodiments 21-22, further comprisingusing a forming die to minimize sideways deformation.

Embodiment 24

The method according to any of embodiments 21-23, wherein bending theQPS superconducting cable comprises bending the QPS superconductingcable to an angle of at least 90°.

Embodiment 25

The method according to any of embodiments 21-24, wherein bending theQPS superconducting cable comprises bending the QPS superconductingcable to an angle of 180° or about 180°.

Embodiment 26

The method according to any of embodiments 21-25, wherein a ratio ofradius of curvature (r_(c)) of the bend to sheath radius (r_(s))(r_(c):r_(s)) is 7:1 or less.

Embodiment 27

A method of compacting a sheath of a QPS superconducting cable accordingto any of embodiments 1-20, wherein the method comprises:

drawing the sheath through a forming die in a succession of reducingdeformations until the plurality of superconducting wires (and theplurality of quench heater wires, if present and within the sheath)compress the spring tube by a small displacement so that each of theplurality of superconducting wires (and the plurality of quench heaterwires, if present and within the sheath) are immobilized in an annularspace between the sheath and the spring tube, and each of theneighboring wires of the plurality of superconducting wires (and theplurality of quench heater wires, if present and within the sheath) arecompacted against one another so that a controlled electrical contact isestablished among the neighboring wires of the plurality ofsuperconducting wires (and the plurality of quench heater wires, ifpresent and within the sheath).

Embodiment 28

A C dipole electromagnet, in which two windings of a QPS superconductingcable according to any of embodiments 1-20 (and possibly bent accordingto the method of any of embodiments 21-25) are assembled onto a centralmandrel containing a hollow interior including two hollow interiorchannels connected by a narrow slot aperture, so that when current ispassed through the windings an approximately homogeneous magnetic fieldis produced inside one of the interior channels.

Embodiment 29

The electromagnet according to embodiment 28, wherein the centralmandrel contains sufficient structural strength to form an H-beam bridgeto support the vertical compressive force produced by the magnetic fieldacting back on the two windings so that the narrow slot aperture issupported sufficiently that it deflects by an acceptably small amount.

Embodiment 30

A dipole beam transpolt channel, in which two windings of a QPSsuperconducting cable according to any of embodiments 1-20 (and possiblybent according to the method of any of embodiments 21-25) are assembledonto a central mandrel containing a hollow interior channel, so thatwhen current is passed through the windings an approximately homogeneousmagnetic field is produced inside the interior channel.

Embodiment 31

A quadrupole beam transport channel, in which four windings of a QPSsuperconducting cable according to any of embodiments 1-20 (and possiblybent according to the method of any of embodiments 21-25) are assembledonto a central mandrel containing a hollow interior channel, so thatwhen current is passed through the windings an approximately symmetricquadrupole magnetic field is produced inside the interior channel.

Embodiment 32

A combined-function transport channel, in which the four windings ofembodiment 31 are assembled onto the two windings of embodiment 30 toproduce a superposition of dipole and quadrupole field inside theinterior channel.

Embodiment 33

A solenoid magnet, in which the insulated sheathed cable of embodiment28 is wound onto a mandrel in a cylinder that contains a mold-releasefilm on its outer surface and a slot and spreader bracket so that themandrel can later be removed, then the winding is heat-treated ifnecessary while supported on the mandrel, then an outer split cylindermetal shell is assembled onto the winding and pulled together to form asnug compressive fit, then the split in the shell is welded so that theshell provides a compressive containment of the winding, then the voidspaces of the winding are vacuum impregnated, and the removable mandrelis collapsed and removed.

Embodiment 34

A transmission line, in which three insulated sheathed QPSsuperconducting cables according to any of embodiments 1-20 aresupported in parallel in a triangular array and contained within a metalenclosure.

Embodiment 35

The transmission line according to embodiment 34, wherein each insulatedsheathed cable is wrapped with a spiral wrap of multiple layers of anelectrically insulating paper or polymer.

Embodiment 36

The transmission line according to any of embodiments 34-35, wherein thethree insulated sheathed cables are supported by a row of reinforcedpolymer brackets, each bracket comprising a semi-rigid pattern of ribsthat support the cables in the triangular geometry with respect to oneanother and with equal spacing from the inner walls of the cylindricalmetal shell.

Embodiment 36

The transmission line according to any of embodiments 34-35, wherein themetal enclosure contains two concentric cylindrical metal shells, theinner shell comprising an overlapping interlocking spiral flex tube, theouter one comprising a flexible metal bellows tube that is hermetic tocontain vacuum.

Embodiment 37

The QPS supporting cable according to any of embodiments 1-20, whereinthe cable is an insulated sheathed cable in which the spring tube is asupport spider containing a central hole for cryogen flow and amultiplicity of open-side support channels (perforations), whereininsulated sheathed cables are inserted from the side into the supportchannels, a conformal shoe is place over the outside of each cable, theassembly is pulled through the sheath tube, and the sheath tube is drawndown onto the support spider so that each cable is immobilized withinits support channel.

A greater understanding of the present invention and of its manyadvantages may be had from the following examples, given by way ofillustration. The following examples are illustrative of some of themethods, applications, embodiments and variants of the presentinvention. They are, of course, not to be considered as limiting theinvention. Numerous changes and modifications can be made with respectto the invention.

Example 1

A QPS superconducting cable as described herein was fabricated, whereinthe superconducting wires included NbTi, and used for a 4.5 Tesla (T)dipole magnet as a basis for a 100 tera-electronvolt (TeV) hadroncollider. FIG. 5 shows a cross-sectional view (left) and schematic view(right) of the 4.5 T superferric dipole using pancake QPS windings.Referring to FIG. 5, the 4.5 T superferric dipole 600 was designed,using the QPS superconducting cable, as a cost-minimum basis forbuilding a 100 TeV hadron collider for high energy physics research.Each dipole 600 was configured in a C geometry 606 so that thehorizontal fan of synchrotron radiation exited the beam tube through aslot aperture and could be absorbed in a separately cooled radiationchannel. The radiation channel contained NEG vacuum pumping and wascooled at about 150 K by separate cooling tubes so the about 20 Wattsper meter per bore (W/m/bore) of synchrotron radiation heat could beremoved without major power requirement.

By separating the heat from synchrotron light and the associated gasdesorption from the beam tube, their effects could be removed from thecirculating beam that could otherwise limit the achievable luminosity.The principle parameters of the dipole are summarized in Table 2. For adipole field strength of 4.5 T, the C geometry 606 requires no moresuperconductor than would a conventional dipole. The windings for eachdipole were fabricated from two lengths of QPS superconducting cable asdemonstrated in FIG. 5 (606). The magnetic design supports 5.0 Tshort-sample field, and operated at 4.5 T with 20 kilo-amp (kA) coilcurrent. FIG. 6 shows the simulated temperature distribution in thewindings in the presence of the heat deposition from beam losses in the100 TeV hadron collider. The cryogen flowing through the QPS cable iscrucial to prevent or inhibit temperature gradients. FIG. 7 shows thecalculated stress distribution in the impregnated windings of theQPS-based dipole. The stress management provided by the sheaths preventsor inhibits stress damage to the cables.

TABLE 2 Principle parameters of the dipole Operating bore field 4.5 T #turns 20 NbTi/Cu wire diameter 1.2 mm Operating current 20 kAShort-sample bore field 5.0 T Physical aperture 3.5 × 2.5 cm² Dipolelength 20 m Inductance 0.3 mH/m Stored energy 63 kJ/m LHe flow inwindings 32 cm³/s Operaturing temperature 4.2-4.3 K Max temp in quench115 K

Example 2

A QPS superconducting cable as described herein was fabricated, whereinthe superconducting wires included MgB₂, and used for compact beamgantries for proton beam therapy (PBT) for cancer. PBT provideslocalized dose (Bragg peak) to kill cancer cells in a tumor with minimumcollateral damage to surrounding healthy tissue. This beneficialtechnique has remarkable results and is a rapidly growing method forcancer therapy. The biggest challenges to its broader adoption are itscapital cost and the time required to treat each patient. Cost isdominated by the size and mass of the beam transport gantries. Treatmenttime is complicated by the difficulty in tuning the transport opticsover a stepped range of proton energies.

Many different designs have been proposed for superconducting beamtransport and gantries for PBT. They share two limitations that havethus far inhibited their development into practice. First, most designsutilize a NbTi superconductor that requires liquid helium refrigeration.Such refrigeration is expensive, inefficient, and problematic for use ona rotating gantry. Second, energy stepping requires rapid re-tuning ofthe gantry for a progression of momenta, and rapid stepping ofsuperconducting magnets is limited by alternating current losses andstepping transients.

A QPS superconducting cable according to an embodiment of the subjectinvention was used to design a superconducting magnet and a beamtransport lattice for the beam gantry that addresses the foregoinglimitations. The QPS superconducting cable based dipole/quadrupole beamtransport magnet integrates the bending and focusing elements of beamtransport in a common magnetic envelope. The QPS superconducting cablebased dipole/quadrupole uses the QPS superconducting cable conductor andpersistent switch/flux pump current management to make a stand-alone,low-mass beam transport system with integrated cryo-cooler. The QPSsuperconducting cable based design supports optimum, compact optics forpencil-beam therapy and rapid energy stepping. Several factors makethese magnets ideal for PBT optics. First, the gantry has ⅕ the mass ofconventional optics: about 10 tons for full gantry versus greater than50 tons. Second, the MgB₂ QPS windings integrate 15 K He gas coolingwithin the cable, dramatically reducing the cost and complexity ofcryogenics. Third, the dipole bends and quadrupole focusing areintegrated to provide compact, achromatic, sharp-focus 2-D-scan opticsover a wide focal field. Fourth, a flux-pump and fast-energy-stepping(FP/ES) power source eliminates expensive high-current supplies andprovides about 10 step/second energy modulation for 3-D rastering. Twogantry magnets fashioned from QPS superconducting cable were designed: a2 T field with a 1.2 m bend radius for 250 MeV proton therapy, and a 3 Tfield with 2.2 m bend radius for 450 MeV/c C⁶⁺ therapy. FIG. 13 showsimages of the gantry for C6+ therapy (left), quadrupole windingsproviding focusing optics (second from left), dipole field providingbending (third from left), flair ends of the CIC windings and the CICcable cross section (fourth from left), and the CIC cable bent 180degrees to show mechanical and electrical integrity (right).

Example 3

A QPS superconducting cable as described herein was fabricated and usedfor a superconducting magnetic energy storage (SMES) unit. FIG. 8A showsa schematic view of an SMES unit fashioned from a QPS superconductingcable according to an embodiment of the subject invention. Referring toFIG. 8A, the SMES unit 1002 included an end-connected string of solenoidmodules, with a wedge-shaped steel plate on each end. The SMES unit 1002can connect 64 modules, each with a radius of 3 meters and a length of 4meters, to form a 45-m radius toroid. Using a single layer of QPSsuperconducting cable containing 25 MgB₂ superconducting wires, the unitoperated at 3 T bore field, contained N=200 turns of cable carrying 50kA of current, and stored 2 megawatt-hours (MWh) of field energy. Thechoice of 3 T field requires a much larger footprint for a given storedenergy, but it makes many aspects of construction and operationdramatically simpler than for any high-field SMES design. One of themost important issues for stable operation of the coil is the outwardmagnetic pressure produced by the Lorentz force of the field acting onthe winding: S=B²/(2μo)=3.6 MPa.

That force would produce unacceptable strain in the QPS superconductingcable if the QPS superconducting cable were unsupported. However, asdesigned, the QPS superconducting cable was supported within a 7-cmthick cylindrical aluminum shell (gray), which was closed and weldedover the finished coil to make a snug fit to the helical winding.Aluminum contracts more when it is cooled to cryogenic temperature thandoes the Monel-sheathed QPS superconducting cable (a fractionaldifferential of about 0.001) so that it actually preloads the windingunder compression. When the winding is energized to full current, theLorentz load produces a strain in the aluminum of about 0.001, whichcancels the preload but leaves the coil without any strain degradation.Quench protection was provided by 16 quench heater wires 1006, thermallysunk to all windings. FIG. 8B shows an overhead image of the financialdistrict in New York City, with locations of two parks circled (upperleft and lower right), each park having a tunnel with an SMES unitlocated therein.

Example 4

A QPS superconducting cable as described herein was fabricated and usedfor a high power transmission line. Superconducting transmission linesfor high-power alternating current (AC) and direct current (DC)connection of electric grids have been a long-standing goal ofdevelopment. FIGS. 9A and 9B show a superconducting transmission line1100 based upon QPS superconducting cables 1104 of an embodiment of thesubject invention. The QPS superconducting cables 1104 operated at 20 K,and the QPS superconducting cables 1104 were cooled by liquid hydrogenoperating in a closed-loop cryo-cooler. The required current-carryingperformance was accommodated at that temperature using MgB₂, and liquidhydrogen is an excellent cryogenic fluid for refrigeration (large heatcapacity, and two-phase flow can be taken advantage of). Moreover, asupport spider 1112, made of injection-molded powder- orfiber-reinforced polymer, maintained the QPS superconducting cable 1104geometry with respect to one another and within the flexible QPSsuperconducting cable 1104. The support spider 1112 is an importantelement in maintaining flexibility in the finished QPS superconductingcable 1104, so that it can be transported on a spool (radius of about 4m) and field-installed flexibly. The support spider 1112 helped enablethe assembly of three QPS superconducting cables 1104 onto the supportspider 1112 as a subassembly, and then the subassembly was slid into the2-shell outer sheath 1108, the complete assembly 1100 of which is shownin FIG. 9A. Quench protection was provided by cabling quench heaterwires along with the superconducting wires, as shown in FIG. 1.

Example 5

The windings of high-field solenoids or toroids typically require manylayers of cable turns, wound one upon the other as a capstan. Examplesare the high-field toroids and ramped solenoids for tokomaks, and thehigh-field solenoids for magnetic resonance spectroscopy. Theaccumulation of hoop compression from capstan winding, coupled with theaccumulation of hoop tension from the Lorentz forces on all layersduring operation, combine to make a pattern of stress that requires ahigh-modulus structure distributed within the winding.

FIGS. 10A and 10B show a design for a 40 kA QPS superconducting cable1202 suitable for use in solenoid applications including but not limitedto the International Thermonuclear Experimental Reactor (ITER) centralsolenoid (CS). The strands are the same size as those used in CS, thecable is composed of six 7,500 A sub-cables, and the sub-cables areseparately supported within the square armor jacket by means of asupport spider in the bore. The support spider was fabricated with atwist pitch suitable for controlling redistribution of chargingcurrents, and the sub-cables were laid into the spider during cablingwith twist pitch.

Two methods were used for cabling the sub-cables. FIG. 10A showssub-cables that are low-void-fraction ropes 1202. FIG. 10B shows acoherent cabling of nearly square strands around a secondary center tubecore 1206. The support spider and the armor jacket can be comprised of316LN or equivalent high-strength alloy. The spider is highly effectivein stiffening the cable against deformation under hoop stress andcompressive stress. The support spider can be drilled radially toprovide flow channels through which supercritical He can flow betweenthe central flow channel and the sub-cable spaces. If the sub-cables aremade by coherent winding, the center tubes within each sub-cable aresimilarly drilled to provide distributed He flow paths. The shaped stripthat supports the cable against the jacket wall can be drilled and givenbeveled corners to provide He flow channels on the corners 1206. FIG. 14shows alternative options for forming the continuous support spider fromsix 316LN T-sections. The T-sections can be fabricated (e.g., in about6-m lengths), fed to the assembly head at a tilt angle that naturallyforms the desired spiral pitch, and the cross-flats of neighboringT-sections can be welded together at the assembly head, either ascontinuous or section welds. A pattern of He flow channels can bedrilled radially through the weld regions to provide for He flow.

The ITER CS utilizes a 45 kA Nb₃Sn cable-in-conduit conductor in whichthe superconducting wires are braded into ropes and the ropes arebraided into a rope-on-rope configuration. FIG. 15 shows a schematicview of the rope-on-rope configuration of the ITER CS, demonstratingthat each strand crosses over neighbors at random locations and thespacing between crossovers varies stochastically from a few cm to manycm. This arrangement gives rise to two problematic situations: first,each crossover presents a stress concentration where the two strandscontact, at which local stress can be large by an order of magnitudethan average stresses on strands; second, between successive crossovers,each strand is unsupported. The alternative concept discussed in thisexample address these issues.

Prototype cables were tested under cyclic excitation (10,000 cyclestotal) to simulate the internal strain that is exerted upon strandswithin a rope-fabricated cable. As depicted in FIGS. 10A and 10B, thehigh-modulus support spider provides stress management within each QPSsuperconducting cable so that capstan and hoop stress are supported bythe spider and not passed to the QPS superconducting cables within. FIG.11 shows a method for assembly of the QPS superconducting cable. First,six QPS superconducting cables were fed into their slots in the supportspider. Support shoes (red) were located over the open side of eachslot, and then the armor jacket was applied, either by welding twoclamshells together or by pulling the spider subassembly into segmentsof cable and drawing the jacket onto the spider subassembly.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication.

All patents, patent applications, provisional applications, andpublications referred to or cited herein (including those in the“References” section) are incorporated by reference in their entirety,including all figures and tables, to the extent they are notinconsistent with the explicit teachings of this specification.

REFERENCES

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What is claimed is:
 1. A quench protected structured (QPS)superconducting cable, comprising: a spring tube; a plurality ofsuperconducting wires disposed around the spring tube; a sheathsurrounding the plurality of superconducting wires and the spring tube;and a plurality of quench heater wires, wherein the spring tubecomprises a plurality of perforations, and wherein each quench heaterwire of the plurality of quench heater wires is a resistive wire thatgenerates heat as current passes through it.
 2. The QPS superconductingcable according to claim 1, wherein the plurality of quench heater wiresare distributed among the plurality of superconducting wires within thesheath.
 3. The QPS superconducting cable according to claim 1, whereinthe plurality of quench heater wires are provided external to thesheath.
 4. The QPS superconducting cable according to claim 3 whereinthe plurality of quench heater wires are distributed on an outer surfaceof the sheath.
 5. The QPS superconducting cable according to claim 1,wherein the superconducting wires of the plurality of superconductingwires are cabled with a twist pitch around the spring tube and areconfined within the sheath.
 6. The QPS superconducting cable of claim 1,wherein the spring tube is filled with a cryogen that passes through theplurality of perforations in the spring tube and thereby fillsinterstitial space between the sheath and the plurality ofsuperconducting wires.
 7. The QPS superconducting cable according toclaim 1, wherein the plurality of superconducting wires includes atleast one of the following materials: NbTi/Cu; Nb₃Sn/Cu; Bi-2212/Ag;MgB₂/Monel; ferropnictide; Bi-2223; YBCO; and rare-earth-based bariumcarbonates (ReBCO).
 8. The QPS superconducting cable according to claim7, wherein each superconducting wire of the plurality of superconductingwires is cylindrical or is a flat ribbon.
 9. The QPS superconductingcable according to claim 2, further comprising at least one layer ofthermally conducting and electrically insulating tape spiral-wrappedaround the plurality of superconducting wires, the plurality of quenchheater wires, and the spring tube within the sheath.
 10. A quenchprotected structured (QPS) superconducting cable, comprising: a springtube; a plurality of superconducting wires disposed around the springtube; and a sheath surrounding the plurality of superconducting wiresand the spring tube, wherein the spring tube comprises a plurality ofperforations, and wherein the QPS superconducting cable furthercomprises a plurality of resistive wires, equal in number to theplurality of superconducting wires, cabled with the plurality ofsuperconducting wires so that a first resistive wire of the plurality ofresistive wires is located at a V-crevice formed between two contiguoussuperconducting wires of the plurality of superconducting wires, so thata radius of an outermost point on the first resistive wire from thecenter of the cable equals the radius of an outermost point on the twocontiguous superconducting wires.
 11. The QPS superconducting cableaccording to claim 10, wherein the plurality of resistive wires iscoated with an insulator.
 12. The QPS superconducting cable according toclaim 10, wherein each resistive wire of the plurality of resistivewires comprises a metal alloy.
 13. The QPS superconducting cableaccording to claim 12, wherein the metal alloy comprises stainless steelof Monel.
 14. The QPS superconducting cable according to claim 11,wherein the insulator is a uniform film of any of a ceramic, a glass,and a polymer.
 15. The QPS superconducting cable according to claim 1,wherein the sheath comprises any one of: a fiber-glass cloth; and afiberglass tape applied to an outer surface of the plurality ofsuperconducting wires.
 16. The QPS superconducting cable of claim 10,wherein the spring tube is filled with a cryogen that passes through theplurality of perforations in the spring tube and thereby fillsinterstitial space between the sheath and the plurality ofsuperconducting wires.
 17. The QPS superconducting cable according toclaim 10, wherein the plurality of superconducting wires includes atleast one of the following materials: NbTi/Cu; Nb₃Sn/Cu; Bi-2212/Ag;MgB₂/Monel; ferropnictide; Bi-2223; YBCO; and rare-earth-based bariumcarbonates (ReBCO).
 18. The QPS superconducting cable according to claim17, wherein each superconducting wire of the plurality ofsuperconducting wires is cylindrical or is a flat ribbon.
 19. The QPSsuperconducting cable according to claim 10, wherein the sheathcomprises any one of: a fiber-glass cloth; and a fiberglass tape appliedto an outer surface of the plurality of superconducting wires.